1. Field of the Invention
The present invention relates to a battery recharging circuit and, more particularly, to a rechargeable flashlight having a dual indicator light for indicating the presence and absence of a charging current.
2. The Prior Art Rechargeable batteries, such as those comprising nickel and cadmium, commonly referred to as a "Ni-Cad", have long been known in the art. Corresponding circuits suitable for recharging such batteries have likewise been developed and widely used. Typically, these prior art circuits operate from a convenient power source, such as household 117 VAC, and include rectifying means, such as a diode or diode bridge, for developing a charging current that is applied to the battery to effect recharging.
It has also been recognized as useful to provide means for indicating that recharging is being successfully carried out by the recharging circuit. For example, a lightbulb driven by the charging circuit has been employed for such purposes. In applications in which a battery is being continuously charged, such as emergency lighting systems or household appliances conveniently readied for immediate use, it is also useful to provide means for indicating absence of charging current due, for example, to failure of the charging circuit. In the case of household appliances, such as rechargeable flashlights, this latter indicating means can be of help in allowing the flashlight to be quickly located in the event of a power failure and, hence, interruption of the charging current.
A battery recharging circuit with indicator lights as disclosed in Nelson et al., U.S. Pat. No. 3,890,555, includes means for indicating both a "CHARGE" condition and a "POWER OFF" condition. The disclosed indicator circuit includes a pair of cross-coupled transistors having a common current limiter, and a separate light emitting diode connected in series with the collector-emitter current path of each transistor. The two transistors are turned on alternately by the charging current or, in the case of failure of the power source, by current discharged by the battery. Driving these two transistors, particularly in the event of a power failure, causes an additional amount of current to be drawn from the battery in excess of the current needed to illuminate the "POWER OFF" indicator. Accordingly, the battery drains faster than is necessary which results in reduced battery charge if the flashlight is to be used and/or abbreviated illumination of the "POWER OFF" indicator. The presence of the cross-coupled transistors also means additional parts necessary for construction of the device, thus raising the costs, both of inventory and labor, associated with the circuit, as well as increasing the number of components subject to failure in the field.